1. Field of the Invention
The present invention relates to a magneto-optical recording apparatus for use with a magneto-optical recording and reproducing apparatus capable of recording and reproducing a magneto-optical recording medium, such as a mini disc (MD) or the like, for example.
2. Description of the Prior Art
Magneto-optical recording and reproducing apparatus that can record and reproduce a magneto-optical disk in 64 mm in diameter accommodated in a disk cartridge, i.e., so-called mini disc (MD), are now commercially available on the market.
FIG. 1 of the accompanying drawings shows a structure of a magneto-optical disk 1 that is recorded and reproduced by this type of magneto-optical recording and reproducing apparatus. As shown in FIG. 1, the magneto-optical disk 1 has a multi-layer structure having a thickness D.sub.1 (D.sub.1 =1.2 mm). Specifically, the magneto-optical disk 1 is formed of 6 layers in which a dielectric layer 3, a recording layer 4 serving as a magnetic film, a dielectric layer 5, a reflection layer 6 and a lubrication protecting layer 7 are laminated on a polycarbonate substrate 2, in that order. A spacing Z.sub.s from the surface of the protecting layer 7 to a center 4c of the recording layer 4 lies in a range of from about 20 to 30 .mu.m.
A magnetic field modulation overwrite head (simply referred to hereinafter as "magnetic head") 8 is disposed in contact with the protecting layer 7 of the magneto-optical disk 1. An optical pickup device 10 of a non-contact type having an objective lens 9 is disposed at the position opposing the magnetic head 8 across the magneto-optical disk 1.
The magnetic head 8 comprises an E-type core 11 having a center core portion 11a shown in FIG. 2 and a winding 13 formed by a plurality of turns of conductors 12 wound on the center core portion 11a.
In the magneto-optical recording and reproducing apparatus thus arranged, the direction of a magnetic field supplied to the recording layer 4 is determined by switching a polarity of a current flowed to the winding 13 from terminals 14 and 15. A magnetization on the recording layer 4 is erased by heating the recording layer 4 at temperature higher than a Curie temperature obtained when the recording layer is radiated with a laser spot L converged by the objective lens 9. If the magneto-optical disk 1 is rotated to move the laser spot L from the recording layer 4 at its portion in which the magnetization was erased, then the temperature at that portion is progressively lowered with the result that the recording layer 4 is magnetized in the direction of the magnetic field supplied to that portion from the magnetic head 8.
At that time, the quality, such as a carrier-to-noise ratio (C/N), of signals obtained when the magneto-optical disk 1 is recorded and reproduced depends considerably on intensity of an external magnetic field supplied to the recording layer 4 of the magneto-optical disk 1 from the magnetic head 8.
To increase the intensity of the external magnetic field supplied to the recording layer 4 of the magneto-optical disk 1, a distance between the tip end of the magnetic head 8, i.e., the tip end (open end side) of the center core portion 11a of the E-type core 11 and the recording layer 4 should be reduced as much as possible because intensity of magnetic field is in inverse proportion to the square of distance.
For this reason, the conventional magneto-optical disk recording and reproducing apparatus is arranged to record an information signal on the magneto-optical disk 1 by sliding the magnetic head 8 while the magnetic head is in contact with the magneto-optical disk 1 as shown in FIG. 1. Even though the magnetic head 8 is brought in contact with the magneto-optical disk 1, the magnetic head 8 is slid in contact with the protecting layer 7 in actual practice, keeping the spacing Z.sub.s corresponding to the thicknesses of the dielectric layer 5, the reflection layer 6 and the protecting layer 7 left between the magnetic head 8 and the center 4c of the recording layer 4.
FIG. 3 is a graph showing a relationship between the magnetic head 8 and the C/N. In FIG. 3, a horizontal axis represents a spacing Z distant from the center 4c of the recording layer 4 where the center 4c of the recording layer 4 is assumed to be zero. A vertical axis represents a C/N. In FIG. 3, reference symbol E represents a characteristic of the magnetic head 8 obtained when the E-type core 11 shown in FIG. 2 is used. A value TL on the vertical axis represents a C/N value that is required to obtain a satisfactory error rate upon playback. A specific value of TL is 46 dB. On the horizontal axis, a value Z.sub.s represents a spacing (approximately 20 to 30 .mu.m in actual practice) from the center 4c of the recording layer 4 to the surface of the protecting layer 7 shown in FIG. 1. Study of FIG. 3 reveals that the magnetic head 8 of the contact sliding type using the E-type core 11 shown in FIG. 2 can produce a C/N sufficiently higher than the C/N value TL which is needed to obtain a satisfactory error rate.
A force to urge the magnetic head 8 against the magneto-optical disk 1 should preferably be made as small as possible because such small force cannot substantially affect the rotation of the magneto-optical disk 1, i.e., a load on a spindle motor (not shown) is small. For this reason, the weight of the magnetic head 8 is limited to a certain extent. Also, the diameter of the E-type core 11 and the number of turns of the conductor 12 are limited.
As shown in FIG. 4, when the magnetic head 8 is brought in slidable contact with the magneto-optical disk 1, it is frequently observed that the magneto-optical disk 1 is rotated with a disk surface fluctuation m (see FIG. 4) in the axial direction (upper and lower direction) of the magneto-optical disk 1 because the thickness of the magneto-optical disk 1 is not uniform and the magneto-optical disk 1 has an inclination. To remove such disk surface fluctuation m, the magnetic head 8 is constantly spring-biased in the arrow K direction (i.e., the axial direction of the magneto-optical disk 1) through a supporting arm 18 serving as a spring member from a fixed member 17. With this arrangement, the magnetic head 8 can reliably be brought in slidable contact with the disk surface of the magneto-optical disk 1 following the disk surface fluctuation m. As a consequence, a pushing force for urging the magnetic head 8 against the magneto-optical disk 1 cannot be decreased sufficiently.
It has been customary for the user to carry the magneto-optical disk recording and reproducing apparatus when in use. Therefore, it has been requested so far that the magneto-optical disk recording and reproducing apparatus should be made small, light, thin and low in power consumption.
Since however the conventional magneto-optical disk recording and reproducing apparatus is arranged such that the magnetic head 8 is brought in slidable contact with the magneto-optical disk 1, a relatively large load is imposed upon the spindle motor (not shown). Thus, it is difficult to reduce the power consumption of the conventional magneto-optical disk recording and reproducing apparatus.
Further, since the conventional magneto-optical disk recording and reproducing apparatus is of the slidable contact type, it cannot be ensured that the magneto-optical disk recording and reproducing apparatus is reliable under undesirable circumstance, such as dusty circumstance or the like. Further, since the magnetic head 8 is brought in contact with the magneto-optical disk 1 in use, the magnetic head 8 tends to be worn.
To solve the problem that the conventional magneto-optical disk recording and reproducing apparatus is not so high in reliability, it is proposed to construct a magneto-optical disk recording and reproducing apparatus as a non-contact type by spacing the magneto-optical disk 1 and the magnetic head 8 apart from each other with a predetermined distance under servo control. This non-contact type of the magneto-optical disk recording and reproducing apparatus needs an actuator and a servo circuit. Therefore, unavoidably, the proposed magneto-optical disk recording and reproducing apparatus cannot be made small, light, thin and low in power consumption.